Powers of sqrt(13) rounded up.

Terms

a(0) =1a(1) =4a(2) =13a(3) =47a(4) =169a(5) =610a(6) =2197a(7) =7922a(8) =28561a(9) =102979a(10) =371293a(11) =1338716a(12) =4826809a(13) =17403308a(14) =62748517a(15) =226242996a(16) =815730721a(17) =2941158942a(18) =10604499373a(19) =38235066240a(20) =137858491849a(21) =497055861120